Speleogenesis on Cayman Brae, Cayman Islands, British West Indies

Abstract

<p>Due to differential tectonic uplift the core of Cayman Brac (Tertiary dolostone of the Bluff Group) reaches - 45 m in the east and is overlain by the Pleistocene limestone, the Ironshore Formation, in the west. The Bluff Group creates a cliff along most of the island in which an erosional notch of the last interglacial period is present at about 6 m amsl. The entrances of the caves are in the cliff, rarely on the plateau. The notch caves lie a few meters above the notch and show a similar morphology: smooth rounded walls, bellholes and not much speleothem. The higher caves differ in morphology and speleothem abundance. Tibbetts Turn Cave shows morphological similarities with the notch caves but contains much more speleothems, which could indicate that it is older. Little Cayman Brac Cave follows a pre-existing vertical joint pattern sub-parallel to the cliff. The passages in Peter's Cave are also sub- parallel but appear to be determined by an arching joint. Dating of the speleothems revealed that speleothem growth was not continuous over time and that the periods of growth cessation or dissolution were not necessarily linked to the glacial-interglacial sequence of the Quaternary. Periods of growth cessation were dated at > 350 ka, - 200 ka and 75-20 ka. The present is for the majority of the speleothems a period of growth cessation. In the caves three different speleothem dissolution types were identified. Type 1 consist of speleothem that has lost its initial morphology and is dissolved in the same manner as the walls in which they are present. Type 2 speleothems have lost an extensive part of their volume but their original morphology is still recognisable. Finally, Type 3 speleothems, often still actively growing, only show point dissolution or none at all.</p>